1. Field of the Invention
This invention relates to integrated circuit (IC) interconnections. More particularly, it relates to IC interconnections utilizing a heated ultrasonic transducer.
2. Description of the Prior Art
Conventional bonding temperatures for IC interconnections typically range between 250.degree. C. to 380.degree. C. This temperature range limits the kind of plating materials which can be used in the fabrication of leadframes. Use of lower-melting point materials such as tin or solder would not only reduce the cost of raw materials for plating but would also give generally greater flexibility in the processing of the integrated circuit (i.e. if temperatures of 250.degree. C. to 380.degree. C. did not have to be obtained for IC bonding).
Thus the existing process temperature for IC bonding, limits the use of materials other than those generally used now such as silver, nickel, copper, alloy 42, etc.
Conventional processes such as thermosonic or thermocompression methods achieve the high temperatures needed for IC interconnection substantially by heating the integrated circuit and the leadframe with a heater block which provides the heat necessary to get good ball bonds and stitch bonds. Thus, the temperature of the IC chip and the leadframe are essentially at the same temperature as required for the IC interconnection bonding because the chip and leadframe are mounted on the heater block surface.
What is needed is a process wherein the leadframe and IC chip can be maintained at a lower temperature so that more economical materials can be used. Another desirable aspect of lowering the temperature would be to achieve greater processing flexibility, as mentioned above.